This article explains AAC files, how to open them, and how to convert them to another audio file format.
How to Convert AAC Files to MP3
A file with the AAC file extension is an MPEG-2 Advanced Audio Coding file. It is similar to the MP3 audio format, but contains some performance improvements.
Apple's iTunes and iTunes Store use Advanced Audio Coding as their default encoding method for music files. It is also the default audio format for many other devices and platforms.
AAC files can almost certainly have the .AAC file extension, but they are more commonly found within the M4A file container and therefore usually have that file extension.
